The invention is related to the field of detection of radioactive contamination sources and the presence of radioactive materials in moving objects, and is designed for complexes and systems of radiation monitoring used in dosimetric customs and security services related to tasks of nuclear safety and State Atom Inspection.
For detection of fast neutrons, the technologies generally used are organic hydrogen-containing materials based on plastics (CH), or stilbene [Patent of Russian Federation No. 2088952, G01T 1/20], or helium counters [V. I. Ivanov, Course of Dosimetry, Moscow: Energoatomizdat, 1988, p. 399]. For detection of thermal neutrons, scintillation crystal 6Li(Eu) containing 6Li is used [Yu. K. Akimov, Scintillation methods for detection of high energy particles, Moscow: Ed. Moscow State University, 1963]. This scintillator, however, has low detection efficiency of fast neutrons and is also highly hygroscopic, which hinders its broad application.
The detection efficiency with these materials does not exceed 1-10%.
A method for detection of fast neutrons is known [Patent of Russian Federation No. 2129289, G01T 1/167], based on the mechanism of elastic scattering of fast neutrons in a hydrogen-containing material with subsequent recording of “thermal” neutrons by 3He-based counters. Signals obtained in the counters are amplified to the required level, and counter pulses are formed with frequency proportional to the neutron flux, with subsequent detection of neutrons using appropriate algorithms.
The efficiency of methods using the elastic scattering mechanism does not exceed 10%, and for reliable detection of weak fluxes of fast neutrons, detector panels of large volume, area, and weight are to be used. Thus, neutron detectors based on 3He-counters used in the “Yantar” system produced by “ASPEKT” involves 8 tubes filled with 3He, with dimensions Ø30×900 mm, placed in a polyethylene moderator. The efficiency of fast neutron detection using this method is 8%. The sensitivity of the detector panel of 120×100×1000 mm dimensions is 350 pulses-cm2/neutron·s, and weight is 130 kg.
Another known method of fast neutron detection [Data sheet of NUCSAFE ins. Last modified, Oct. 29, 2007] is based on elastic scattering of fast neutrons in hydrogen-containing material with subsequent recording of “thermal” and “slow” neutrons by a scintillating glass fiber placed in a hydrogen-containing material. Signals recorded in the scintillating glass fiber are amplified to the required level, counting pulses are shaped with frequency proportional to the neutron flux, and neutrons are detected according to the appropriate algorithm.
However, as in the first method, ensuring high sensitivity to fast neutrons requires the use of moderators made of hydrogen-containing material. Because the scintillation glass fiber has low sensitivity to fast neutrons, obtaining the desired sensitivity requires the use of detector panels of large volume, area and, consequently, weight. The efficiency of fast neutron detection by this method also does not exceed 8%. The sensitivity of a detector panel of 1000 to 6000 cm2 area is ˜300 pulses-cm2/neutron·s.
Still another known method of fast neutron detection [M. Anelli., G. Battistoni, C. Bini, et. al., Measurement and simulation of the neutron response and detection efficiency of a Pb-scintillating fiber calorimeter, Nuclear Instruments and Methods in Physics Research A 581 (2007) 368-372] is based on inelastic scattering of fast neutrons in lead, which is used as a converter. 200 layers of lead foil of 0.5 mm thickness are used, in the grooves of which fiber organic scintillators are placed, and signals are recorded that result from interaction of organic fiber scintillators with cascades of gamma-quanta formed due to inelastic scattering of neutrons in the lead foil (converter). Then their full analysis is carried out with subsequent conversion of the obtained information into a digital code using 40+40 blocks of analog-to-digital converters. The obtained data array is written onto a digital carrier and is processed using powerful computers. Then counting pulses are formed with frequency proportional to the neutron flux, counting rate is calculated depending on the neutron flux, and neutrons are recorded according to the appropriate algorithm.
However, this method of fast neutron detection is rather complex and labor-consuming, because it requires full analysis of all signals emerging from the interaction of fast neutrons with the converter (the presence of which increases the detector size), preliminary recording of intermediary data onto the information carrier and subsequent data processing using powerful computers. This makes this method not suitable for its use in radioactive materials detection systems operating on the real time scale.
The last of these analogs has been chosen as a prototype.